Prevention of Overfeeding During Infancy This application addresses broad Challenge Area (01) Behavior, Behavioral Change, and Prevention and specific Challenge Topic, 01-DK-102: Discovery of Behavioral Mechanisms Relevant to Obesity. It is becoming increasingly evident that prevention of child obesity must begin very early in life, as the prevalence of child overweight in the U.S. in the past 20 years has increased even in the youngest age groups. One of the key risk factors for later obesity is a rapid rate of weight gain during infancy;related behavioral factors are parenting styles and associated infant feeding practices. Overfeeding of infants, particularly those who are bottle-fed, presumably contributes to rapid weight gain, but there is little information on how to effectively address this issue. It is well-documented that formula-fed infants consume more energy and gain more weight than breastfed infants, even during the first few months of life. Furthermore, breastfed infants have a lower risk of developing child obesity, although the mechanisms for this remain unclear. One potential mechanism is that being fed from a bottle may encourage excessive intake. Infants who feed at the breast are able to self-regulate intake based on internal satiety cues, but bottle- feeding creates the possibility of overfeeding. The overall goal of this project is to identify strategies to prevent overfeeding during infancy. One objective is to evaluate the impact on intake of allowing the infant greater control over the amount consumed when feeding from a bottle. This will be accomplished via the use of a novel nipple that mimics (functionally) the nipple of a human breast and allows the infant to self-regulate milk flow. The second objective is to evaluate the relationship between parental feeding styles and infant intake. In one arm of the study, formula-fed infants will be randomly assigned to use the novel nipple or a conventional nipple. We hypothesize that a) infants randomized to be fed with the novel nipple will have a lower intake per feed compared to infants randomized to use a conventional nipple, and b) infants of parents with an authoritarian feeding style will have a higher intake of formula per feed compared with children of parents with non- authoritarian feeding styles. Additional outcomes include 24-h intake, infant weight gain, and caregiver-reported infant fussiness. The other arm of the study will be conducted with infants who are fed human milk both at the breast and with a bottle. In that cohort, we will a) compare intake of human milk at the breast to intake of expressed human milk fed by bottle, b) evaluate whether the intake of human milk fed by bottle is different when using the novel nipple compared to a conventional nipple, and c) examine whether parental feeding style is related to infant intake. We hypothesize that intake per feed will be lower when fed at the breast than when fed by bottle and also lower when using the novel nipple compared to a conventional nipple, and that intake of human milk-fed infants is not related to parental feeding style. Mothers who plan to use a bottle within the first 3 months to feed their infants either breast milk or formula will be recruited before discharge from the maternity ward of the University of California, Davis Medical Center. Infants will be randomized to the novel nipple or the conventional nipple, and a supply of bottles and nipples will be provided to the mother. Biweekly contact will be maintained with the mother throughout the study. At two time points, when the baby is 3 and 4 months old, the mother will complete a 48-hour weighed record of infant milk/formula intake (including test-weighing before and after all breast feeds). A research assistant will measure the infant's weight and length, and conduct an exit interview to evaluate caregivers'feeding style and their perceptions of the nipple to which they were assigned and their infant's feeding patterns and growth. The target sample size is 110 formula-fed (or mixed- fed) infants and 110 infants fed exclusively breast milk at ~ 4 mo. The results of the study will provide important evidence regarding the reasons for the difference in intake between formula-fed and breastfed infants, which is critical for designing effective interventions to reduce overfeeding during infancy and subsequent child obesity. Childhood obesity has reached epidemic proportions in the U.S., and the need for prevention very early in life is evident given that one-fourth of children aged 2-5 years are overweight or obese. Overfeeding during infancy undoubtedly contributes to child obesity, but the factors leading to overfeeding are not well understood. The proposed study will advance our understanding of the behavioral factors affecting infant intake, thereby facilitating the development of effective tools and strategies for prevention of child obesity.